Method for removing contaimination from precipitates



States of America as represented by the United States Atomic EnergyCommission N Drawing. Application September 7, 1951 Serial No. 245,637

11 Claims. (Cl. 2314.5)

The present invention relates in general to improvements in processesfor the production of plutonium, and more particularly to a washingmethod for the removal of contamination, especially uranium fissionproducts, from carrier precipitates, bearing plutonium values, which arecontaminated therewith.

As is known, plutonium-*more specifically the 239 isotope ofplutonium-is conventionally produced by transmutation of uraniumefiected by subjecting natural uranium to neutron irradiation. Incurrent practice, the product thus obtained is ordinarily a mass ofirradiated uranium containing a concentration of the order of 0.02%plutonium and a like concentration of uranium fission products. However,the presence of even small amounts of uranium or fission productsusually interferes with the ultimate applications of plutonium. This isespecially true with respect to the fission productsisotopes havingatomic numbers ranging predominantly from 30 to 63which are in generalhighly radioactive and there fore greatly deleterious from bothphysiological and technical standpoints. Accordingly, for successfulutilization, the small proportion of plutonium so produced must beisolated and recovered from the materials associated with it in theirridated mass.

Employing customary procedures, initially the plutonium, accompanied bymuch of the fission product contamination, is quite readily separatedfrom the bulk of uranium. This may be done by dissolving the irradiatedmass in aqueous nitric acid, solubly complexing uranium with sulfateion, and removing from solution the oftenminute concentration ofplutonium in its tetravalent state by carrier precipitation upon bismuthphosphate. Then, for the exceedingly diificult tasks of isolatingplutonium from the fission product contamination and concentrating theso decontaminated plutonium, conventional procedures involve pluralitiesof cycles of separate selective carrier prccipitations of plutonium andof fission products from aqueous solution. Preeminent among such carrierprecipitation cycles are those employing bismuth phosphate and thoseemploying lanthanum fluoride: first to selectively carry plutonium andthen, under altered conditions, to selectively carry fission products.It is with such carrier precipitation operations, especially thoseemploying bismuth phosphate, that the present invention is concerned.

Considering the general, conventional bismuth phosphate cycle in greaterdetail, bismuth phosphate characteristically carrier precipitatestetravalent plutonium highly efiiciently, but leaves hexavalentplutonium remaining in solution. Concurrently, bismuth phosphate carriessome fission product species and other contaminants well, and somepoorly, under both plutonium oxidation conditions involved. By virtue ofthese considerations, processing plutonium through successive bismuthphosphate carrier precipitation operations while alternating theplutonium oxidation state between the tetravalent and hexavalent stateswill gradually reduce the fission product contamination. That is, inmore detail, bismuth phosphate is precipitated in an aqueous nitric acidsolution containing the plutonium in tetravalent state, whence plu-Fatented Jan. 6, 1959 add tonium is co-precipitated, leaving behind insolution a substantial portion of fission products and other sources ofcontamination; the carrier precipitate containing plutonium is thenseparated from its supernatant, dissolved to form an aqueous nitric acidsolution and the plutonium oxidized to the hexavalent state. In theresulting solution, bismuth phosphate is again precipitated, ordinarilycarrying down a substantial portion of fission products and othercontaminants, and leaving a preponderant portion of the plutonium insolution. After removing the resulting contaminant-bearing precipitate,the supernatant solution, containing the bulk of the original plutonium,may be treated by another bismuth phosphate carrier precipitation ofplutonium in tetravalent state, or other plutonium purificationoperation. This cycle, comprising alternately carrier precipitatingplutonium, and carrier precipitating contaminants, is conventionallyrepeated a number of times until sufiicient plutonium decontamination iseffected. The general aspects of the lanthanum fluoride cycle aresubstantially identical with those just outlined for the bismuthphosphate cycle. These general cycles comprise the inventions andconcepts of others, and do not, per se, constitute a part of the presentinvention. Details of these processes are more fully set forth incopending applications as for example: S. N. 478,570, filed March 9,1943, now Patent No. 2,799,553, granted July 16, 1957, and 519,714,filed January 26, 1944, now Patent No. 2,785,951, granted March 19,1957, both in the names of Thompson and Seaborg, and in applicantsco-pending application S. N. 597,593, filed June 4, 1945, for Use ofFlue-Reagent, now titled Enhancing Precipitations by Applying SolubleComplex Fluorine-Containing Reagents. Accordingly, reference is made tothese co-pending applications, and as well to the specific exampleshereinafter presented, for further details concerning these conventionalprocesses.

While such carrier precipitation procedures ultimately producesubstantially pure plutonium, their efiiciency could desirably be muchhigher. This results from the fact that in both the plutonium, and thecontaminant, carrier precipitations a considerable portion of thecontaminants, especially gamma-radiation emitters, ordinarily accompanythe plutonium, precipitating with plutonium in the former precipitationand remaining in the supernatant in the latter. Unfortunately, however,with each repetition of a purification cycle for the purpose of furtherpartial removal of the accompanying contamination, an increment ofplutonium is removed with the separated contaminant fraction. As aconsequence, even after its extensive recycling and reprocessing ofcontaminant fractions for plutonium recovery, relatively large amountsof valuable plutonium must finally be discarded with contaminant wastes.Furthermore, since the extreme radioactivity of the fission productsnormally requires that such processing be conducted behind massiveradiation shielding and by remote control techniques until the fissionproduct contamination is reduced to a tolerable radiation level, thepersistence of substantial fission product contamination throughrepeated purification operations has adversely compelled thepurification operations to be encumbered with such apparatus andoperational complexities throughout many stages of processing.Therefore, it has been highly desired, in this particular art, thatefiicient methods for supplementing these conventional carrierprecipitation procedures be found in order to more quickly andthoroughly reduce or eliminate such contamination of plutonium.

Accordingly one object of the present invention is to provide a new andimproved method for removing contamination, particularly contaminatinguranium fission products, from precipitates containing the same.

Another object is to provide such a method particularly adapted toselectively removing such contamination from plutonium-bearing carrierprecipitates, especially bismuth phosphate carrier precipitates,containing the same.

A further object is to provide such a method particularly eifective forremoving gamma radiation emitting species of uranium fission products,so contaminating plutonium-bearing bismuth phosphate carrierprecipitates.

Still another object is to provide such a method adapted to beneficiallysupplement conventional carrier precipitat on procedures so as toincrease decontamination efficiency, toward reducing the number ofcarrier precipitatron cycles required for effective decontamination.

Still a further object is to provide such a method, simple in operation,adapted to be incorporated readily in such conventional procedures witha minimum of equip ment and operational changes.

Additional objects will become apparentihereinafter.

In accordance with the present invention, contaminating uranium fissionproducts are removed from carrier precipitates, especiallyplutonium-bearing bismuth phosphate carrier precipitates, containing thesame, by Washmg the precipitates with an aqueous solution of ammo niumhydrogen fluoride. Applicant has discovered that an aqueous solution ofammonium hydrogen fluoride (this being identical with an aqueoussolution of ammonia and hydrofluoric acid in a molar ratio of 1:2), andsolutions of ammonia and hydrofluoric acid in molar ratios other than1:2, are uniquely effective in washing gamma-radiation-ernitting uraniumfission product contamination from plutonium-bearing bismuth phosphatecarrier precipitates, with very little if any simultaneous removal ofplutonium values therefrom. Not only are such solutions evidentlyselective solventsforthe contaminants but not for the plutonium valuesor the carrier precipitate, but they have further proven not to disruptthe bonding of the minute amounts of plutonium values to theprecipitated carrier compound, even upon a slurrying of the carrierprecipitate therein. For instance, it has been found that three washes,of only one minute each, of a bismuth phosphate carrier precipitatebearing bearing plutonium values and uranium fission products, With anaqueous solution of ammonium hydrogen fluoride (0.5 M in F), removed92.7% of the gamma radiation activity associated therewith, whileremoving only 0.1% of the plutonium values. The utter simplicity of thisoperation makes it readily applicable to conventional carrierprecipitation processes, and it has been found when so applied themethod affords marked increase in the plutonium decontaminationefficiency of those processes, so as to afford reduction in the numberof decontamination stages required and material alleviation of theapparatus and operational complications occasioned by the gammaradioactivity of the contaminants.

In conducting the present process, the exact compositions ofsatisfactory solutions employed for the washing operation are subject toconsiderable variation. It has been found, as an optimum, that solutionsof ammonia and hydrofluoric acid in molar ratio of 1:2 (such being, ineffect, solutions of the compound, ammonium hydrogen fluoride, NH HF arethe compositions generally affording the best decontamination. Yet, gooddecontamination factors are obtainable upon washing with solution ofdifferent NH to HF molar ratios (such being, in effect, solutions ofammonium hydrogen fluoride also containing either ammonia orhydrofluoric acid); among these NH to HP ratios of the order of 1:2 to1:4 are found preferable. Likewise, various wash-solution concentrationsmay be used; while concentrations within the approximate range of to (byweight) are deemed preferable, with 10% appearing to be the optimum,effective results have been obtained with solutions ,even more dilutethan 1%. In general, the washing operation proceeds quite satisfactorilyat convenient room temperature. 7

Since, evidently, no significant disruption of the bonding of theplutonium-values to the bismuth phosphate carrier precipitate obtains,the washing operation itself may be effected by virtually anyconventional precipitate washing procedure. Slurrying the carrierprecipitate with the wash solution, followed by separation of the bulkof the wash liquid, along with the removed contamination containedtherein, from the washed solid by centrifugation, filtration, or thelike, has proven to be eminently satisfactory; preferable slurrying timeis of the order 'of 15 to 30 minutes at room temperature. In particular,in plant-scale plutonium production operations, wherein it is customaryto separate the contaminated, plutoniumbearing carrier precipitate fromthe solution in which it was originally precipitated, by centrifugation,it has been found advantageous merely to add applicants wash solution tothe separated precipitate while it is still in the centrifuge bowl, inamount suflicient to form a loose slurry, and, after several minutescontact in the bowl with mild agitation to keep the precipitatesuspended, centrifuging to separate the solid precipitate from the washsolution. Alternatively, the washing may well be accomplished bypercolating the wash solution through a bed of the precipitate, or byvarious other methods known, or which will immediately become apparent,to those skilled in the art. Although a single wash effects substantialremoval of the contamination, ordinarily even more contamination may beremoved by repetition of the washing operation. In employing suchmultiple washing procedure, three washings appears to be the optimumnumber. It is normallydesirable that the washing with applicantsreagents be followed by a washing with water to purge the precipitate ofany remaining wash solution and any contamination that may be dissolvedtherein. Since washing the carrier precipitates with water is a practiceofttimes includedin conventional operation, applicants washing methodmay be incorpatedin lieu of or supplementary to such conventional waterwashing; in fact, alteration of existing processing procedures may beminimized, where this is desirable, by merely dissolving applicantsreagentin the water which would otherwise be used alone to wash theprecipitates.

In application .ofthe instant washing method torepetitive bismuthphosphate carrier precipitation cycles in conventional plutoniumdecontamination operations, it is most desirable-that the more highlycontaminated ;plutonium-bearing bismuth phosphate precipitates, evolvedin the earlier stages of the operation, be so washed, in order to morequickly remove the bulk of contamination from association with theplutonium; furthermore, since a reduction of gamma contamination to anorder of at least as low as 1() of.origina1 is generally required inconventional plutonium production, the washing in this manner of everyplutonium-bearing bismuth phosphate precipitate accordingly isparticularly beneficial. However, in such application to conventionaldecontamination cycles it has been found that a special precautionarymeasure is advisable, in view of the fact that there is generally someconversion, in the precipitates, of bismuth phosphate to bismuthtrifluoride, upon washing .with applicants reagents. The degree ofconversion of theprecipitate to fluoride varies, depending upon theextent of washing (volume used, time of contact, number of washes,concentration of the solution, and the like). While there is evidentlyno disrupting of the bonding of the carried plutonium values to theprecipitate, despite this conversion to bismuth trifluoride, thefluoride present in the precipitate may detrimentally interfere in latersteps in the cycle, particularly the subsequent step of carrierprecipitating contaminants with bismuth phosphate while maintaining theplutonium values dissolved in hexavalent oxidation state. It has beenfound, however, that the precipitate is readily purged of fluoride ion,when necessary, by washing with an aqueous alkali hydroxide solution.The bismuth trifluoride precipitate is readily converted in this mannerto a bismuth hydroxide precipitate, whereupon it still retains theplutonium values bound thereto, while the fluoride ions are effectivelycarried away in the hydroxide wash solution, since bismuth hydroxide ismore readily soluble in nitric acid than is bismuth phosphate, suchconversion actually enhances, rather than interferes with, the normalsubsequent dissolution of the plutonium-bearing carrier precipitate inthat acid. A single wash with an aqueous solution of KOH or NaOH solution of concentration of the order of 15% (by weight) has been found tobe satisfactory for this purpose.

Further illustration of the quantitative aspects and preferredconditions and procedures of the present method is provided in thefollowing specific examples. Example 1 demonstrates generally theapplication of the present washing method to a conventional bismuthphosphate carrier precipitation operation for plutonium decontamination,and the relative effectiveness in removing contamination of several ofapplicants reagents as compared with water and hydrofluoric acid.

EXAMPLE 1 A bismuth phosphate precipitate carrying plutonium values andcontaminated with uranium fission products was derived in accordancewith the following conventional procedure:

(a) Natural uranium metal subjected to chain uranium fission reactionfor a period suflicient to transmute approximately 0.025% thereof to Puand stored to permit radioactive decay;

(b) Thereafter, uranium metal dissolved in stoichiometric amount of 13 NHNO then diluted with water to form a 31.4% uranyl nitrate solution;

Solution made 1 N in H 80 0.1 M in NaNO then diluted with water to twiceits volume, and heated to 75 C., to reduce Pu to tetravalent state;

(d) 2.5 grams/liter of Bi+++ added; H PO added to 0.6 M over a period oftwo hours; digested one hour at 75 C.; then the formed BiPO carrierprecipitate sep-. arated from its supernatant by centrifugation.

Equal amounts of the resulting precipitate carrying plutonium values butsubstantially no uranium values, and contaminated with uranium fissionproducts, were washed three times with either water, hydrofluoric acidsolution, or ammonium hydrogen fluoride solution, as indicated. Eachwash was conducted by slurrying the precipitate in approximately 15gallons of the particular wash solution per pound of precipitate forapproximately one minute, and then separating the precipitate from thewash solution by centrifugation. For each wash solution, the amount ofplutonium and gamma contamination removed by the washing procedure wasdetermined analytically; the results are presented in Table 1 below.

Table 1.Washing 0f Pu-carrying BiPO precipitates Percent of Total GammaRun Wash Solution Plutonium Decon- Removed tamtnation in Wash Factor 3Solution H2O (control) 0.3 5. 8 HF 0.5 M (control) 3. 4 7. 4 NH :HF=1:40.0 23.3 1 0. 1 13. 7 1. 9 7. 3 4.1 G.

6 EXAMPLE 2 Runs C and D of Example 1 were repeated, but the washingswere made by slurrying for three 20 minute, instead of 1 minute periods.The gamma activity was measured between each wash; results are presentedin Table 2 below.

Table 2.Distribution of gamma activity throughout precipitate washingThe results in Table 2 illustrate the greater gamma decontaminationafiforded by the longer washing periods. It is also noteworthy thatwhile under. the conditions of extremely short slurrying time in Example1 the solution of molar ratio 1:4 afforded the best decontaminationfactor, yet with the washing period of more practical duration inExample 2, the solution of molar ratio 1:2 (ammonium hydrogen fluoride)exhibited marked superiority.

In both of the foregoing Examples 1 and 2, the washings were made verydilute solutions, i. e. ca. 1% (by weight) concentration. In thefollowing Example 3, the effect of concentration of the wash solution isstudied. Also, in this instance, wash solution volumes of only ca. 1.5gallons per pound of precipitate, found more con venient in plant-scaleoperations for washing directly in the centrifuge bowl, were used.

EXAMPLE 3 A series of plutonium-bearing bismuth phosphate carrierprecipitates were derived in accordance with the procedure outlined inExample 1. In each case the entire precipitate was subjected to 3 washeswith an NH HF solution, followed by a final wash with water, employingthe slurrying procedure employed in the preceding examples. The volumeof wash solution used in each wash was ca. 1.5 gallons per pound ofprecipitate. The washing times were 20 minutes for the first wash, and10 minutes each for the second and third washes; the water wash was ofsimilar short duration. The solution concentrations of 2, 5, 10, and20%, respectively, were employed in the four runs made. The gammadecontamination factors were calculated on the basis of gammacontamination in the original solution of irradiated uranium; thecumulative decontamination factors which had been achieved upon the endof each step are tabulated in Table 3 below.

Table 3.Efiect of NH HF concentration in washing Cumulative GammaDecontamination actors NH4HF2 Concentration (percent by wt.) 2 5 10 20Number of Washes 3 3 3 3 Wash Contact Time (mln.) 20-10-10 2()101020-10-10 20-10-10 Step:

(1) Carrier Precipitation 7. 7 6. 6 6. 6 9. 1 (2) After one wash 8. 4 9.7 17. 2 24.0 (3) After two washes. 8.8 13.6 66 28.2 (4) After threewashes 9. 2 17. 5 31. 4 (5) After three NHiHF: washes plus water wash 9.2 19. 8 146 142 Improvement in Decontamination Factor Due to Washes 1. 23 22 15. 6

7 The preferability of employing wash solution concentrations within therange of 10 to 20%, and the apparent optimum of 10%, are plainlyindicated in Table 3.

Analysis of the ammonium hydrogen fluoride wash -solutions after washinghas revealed that a predominate proportion of the uranium fissionproducts contamination thereby removed consisted of zirconium andniobium species, which species, incidentally, normally constitute overtwo thirds of the gamma contamination normally encountered in plutoniumproduction. The eflicacy of the present process for removingspecifically zirconium and niobium activity is specially studied inExample 4, wherein the combined zirconium and niobium activity wasseparately traced through the washing operation.

EXAMPLE 4 Two bismuth phosphate precipitates carrying plutonium valueswere derived and washed in a manner similar to that employed in Example3; while three .washes with NH HF were employed, no wash with water wasused; washing times were 20, 10, and 10 minutes, respectively, and washsolution volumes were 15, 7.5 and 7.5 gallons per pound of precipitate,respectively. In both cases the washing was done at room temperature.The concentration of ammonium hydrogen fluoride was 0.5 M in eachinstance, and the precipitates were stirred during washing with amechanical stirrer. The amounts of plutonium and of zirconium-niobiumactivity, expressed in percentage of the amount originally presentin theinitial solution of irradiated uranium, were determined and aretabulated in Table 4 below.

Table 4.Remval of zirconium-niobium activity While this invention hasbeen described with particular reference to its application theprocessing of specifically Pa through conventional bismuth phosphatecarrier precipitation cycles, it is inherently of much widerapplicability. The present method is equally as well adapted to suchprocessing of other plutonium isotopes, for .example the non-fissionablePu isotope. Pri valuable as a radioactive tracer, may be derived fromnon-fission able sources through application of bismuth phosphatecarrier precipitation processes wherein the present method may beadvantageously employed for removing contamination associated with theprecipitate. Furthermore, applicability is not at all restricted to theconventional carrier precipitations cycles outlined, but beneficiallyextends to the removal of contamination from plutonium-carryingprecipitates, as exemplified by hismuth phosphate carrier precipitates,generally, irrespective of the specific processes in which they arise.

More broadly, the present invention is not necessarily limitedtoplutonium processing. The invention provides a new and improved methodfor removing contamination, especially gamma-emitting radioactivespecies, from bismuth phosphate and the like carrier precipitates. Assuch, the method is eificacious in accomplishing such results regardlessof whether the precipitates are carrying plutonium or not. For example,this method may be employed for the removal and recovery from bismuthphosphate carrier precipitates of cyclotron-produced radiozirconiumand/or radioniobium values being carried 3 thereupon in theirproduction. Various additional applications of the instant method willbecome apparent to these skilled in the art. It is therefore to beunderstood that all matters contained in the above description andexamples are illustrative only and do not limit the scope of the presentinvention.

Cross-reference is made to applicants co-pending application, Ser. No.597,593, filed June 4, 1945, for Use of Flue-Reagent, directed toimproving similar carrier precipitation operations in different manners,with difierent types of fluorine-containing reagents.

What is claimed is:

.1. A method for removing uranium fission products from a bismuthphosphate carrier precipitate which has carried the same from aqueoussolution therewith, which comprises washing the precipitate with anaqueous solution of ammonium hydrogen fluoride.

2. A method for removing gamma-radioactive uranium fission products froma bismuth phosphate carrier precipitate which has carried the same fromaqueous solution therewith, which comprises washing the precipitate withan aqueous solution of ammonium hydrogen fluoride.

3. A method for removing zirconium values from a bismuth phosphatecarrier precipitate bearing the same, which comprises washing theprecipitate with an aqueous solution of ammonium hydrogen fluoride.

4. A method for removing niobium values from a bismuth phosphate carrierprecipitate bearing the same, which comprises washing the precipitatewith an aqueous solution of ammonium hydrogen fluoride.

5. In a process-for the separation and decontamination of plutoniumvalues from an aqueous solution containing the same together withcontaminating uranium fission products, comprising precipitating bismuthphosphate therein while maintaining said plutonium values in tetravalentoxidation state, to thereby carrier precipitate said plutoniumvaluestherewith, and thereafter separating the resulting plutonium-carryingprecipitate from its supernatant solution, the improved method forremoving contaminating uranium fission products from the separatedcarrier precipitate, which have accompanied the same, which compriseswashing the precipitate with an aqueous solution of ammonium hydrogenfluoride.

6. In a process for the separation and decontamination of plutoniumvalues from an aqueous solution containing the same together withcontaminating uranium fission products, comprising precipitating bismuthphosphate therein while maintaining said plutonium values in tetravalentoxidation state, to thereby carrier precipitate said plutonium valuestherewith, and thereafter separating the resulting plutonium-carryingprecipitate from its supernatant solution, the improved method forremoving con-- taminating uranium fission products from the separatedcarrier precipitate, which have accompanied the same, which compriseswashing the precipitate with an aqueous solution of ammonia andhydrofluoric acid of molar ratio within the approximate range of 1:4 to1:2.

7. In a process for the separation and decontamination of plutoniumvalues from an aqueous solution containing the same together withcontaminating uranium fission products, comprising precipitating bismuthphosphate therein while maintaining said plutonium values in tetravalentstate, to thereby carrier precipitate said plutonium values therewith,and thereafter separating the resulting plutonium-carrying precipitatefrom its supernatant solution, the improved method for removingcontaminating uranium fission products from the separated carrierprecipitate, which have accompanied the same, which comprises washingthe precipitate with an aqueous solution of ammonia and hydrofluoricacid in molar ratio within the approximate range of 1:4 to 1:2, and ofconof plutonium values from an aqueous solution containing the sametogether with contaminating uranium fission products, comprisingprecipitating bismuth phosphate therein while maintaining said plutoniumvalues in tetravalent oxidation state, to thereby carrier precipitatesaid plutonium values therewith, and thereafter separating the resultingplutonium-carrying precipitate from its supernatant solution, theimproved method for removing contaminating uranium fission products fromthe separated carrier precipitate, which have accompanied the same,which comprises washing the precipitate with an aqueous solution ofammonia and hydrofluoric acid of molar ratio within the approximaterange of 1:4 to 1:2, by means of slurrying the precipitate in saidaqueous solution, and thereafter separating the plutonium-carryingprecipitate from the contaminant-containing wash solution.

9. In a process for the separation and decontamination of plutoniumvalues from an aqueous solution containing the same together withcontaminating uranium fission products, comprising precipitating bismuthphosphate therein while maintaining said plutonium values in tetravalentoxidation state, to thereby carrier precipitate said plutonium valuestherewith, and thereafter separating the resulting plutonium-carryingprecipitate from its supernatant solution, the improved method forremoving contaminating uranium fission products from the separatedcarrier precipitate, which have accompanied the same, which comprisessuccessively washing the precipitate a plurality of times with anaqueous solution of ammonia and hydrofluoric acid of molar ratio withinthe approximate range of 1:4 to 1:2, with each washing being conductedby slurrying the precipitate in the wash solution and thereafterseparating the plutonium-carrying precipitate from thecontaminant-containing wash solution.

10. In a process for the separation and decontamination of plutoniumvalues from an aqueous solution containing the same together withcontaminating uranium fission products, comprising precipitating bismuthphosphate therein while maintaining said plutonium values in tetravalentoxidation state, to thereby carrier precipitate said plutonium valuestherewith, and thereafter separating the resulting plutonium-carryingprecipitate from its supernatant solution, the improved method forremoving contaminating uranium fission products from the separatedcarrier precipitate, which have accompanied the same, which compriseswashing the precipitate with an aqueous solution of ammonia andhydrofluoric acid of a molar ratio within the approximate range of 1:4to 1:2, separating the plutonium-bearing precipitate from thecontaminant-containing wash solution, and thereafter washing theseparated precipitate with water.

11. in a process for the separation and decontamination of plutoniumvalues from an aqueous solution containing the same together withcontaminating uranium fission products, comprising precipitating bismuthphosphate therein while maintaining said plutonium values in tetravalentoxidation state, to thereby carrier precipitate said plutonium valuestherewith, and thereafter separating the resulting plutonium-carryingprecipitate from its supernatant solution, the improved method forremoving contaminating uranium fission products from the separatedcarrier precipitate, which have accompanied the same, which compriseswashing the precipitate with an aqueous solution of ammonia andhydrofluoric acid of a molar ratio within the approximate range of 1:4to 1:2, and thereafter washing the plutonium-carrying precipitate, whichhas consequently been subject to some conversion to bismuth trifluoride,with an aqueous solution of an alkali hydroxide, to thereby beneficiallypurge the plutonium-carrying precipitate of fluoride ion.

No references cited.

1. A METHOD FOR REMOVING URANIUM FISSION PRODUCTS FROM A BISMUTHPHOSPHATE CARRIER PRECIPITATE WHICH HAS CARRIED THE SAME FROM AQUEOUSSOLUTION THEREWITH, WHICH COMPRISES WASHING THE PRECIPITATE WITH ANAQUEOUS SOLUTION OF AMMONIUM HYDROGEN FLUORIDE.